SimScale CAE Forum

Multi region mesh problem concerning MRF and cell zone

Hello, I’m trying to simulate forces on a propeller and I used MRF for rotation. The meshing is done but when the simulation begin there is a multi region mesh problem. I don’t understand how to fix this issue.

Here is my project https://www.simscale.com/projects/WarChitect/h-licetipe/

Thanks

Hey @WarChitect,

MRFs are currently not supported for tet-dominant meshes (standard meshing tool). They require a special treatment, where you have to assign a cellzone to the volumes that will be spinning.
Please refer to this tutorial on propellers with MRF. It’s quite similar to your project. Should you have any difficulties, do post an update here.

Edit: Since April/2020 cell zones are also supported by the standard algorithm.

/Ric

Thanks for your reply. I don’t think I understood the tutorial in full but I think that I only need to change the mesh type to an hex-dominant parametric?

Yes, that is a start :wink: (or Hex Parametric for more control)

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From that tutorial. the most important step is to define a cell zone for the MRF.

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YEP, I missed that one in the beginning, it is a very important parameter to select during the meshing process (MRFs need their own ‘With cell zone’ mesh refinement)…

Thanks for your help, I think I did what the turorial said but there is still an error that I don’t understand. Any advice ?

When using the parametric hex-dominant meshing tool without running a volume extraction operation beforehand, you have to click on this button after the mesh is finished:

Your mesh had some issues. The aspect ratio of your cells could be better. You want values close to 1 (cubic cells):

Extending the domain a little bit is also a good idea, to give some room for the flow to settle.

To save you some trouble, I drafted one mesh to get you started, which you can find in this link https://www.simscale.com/workbench/?pid=63269172894931018&mi=spec%3A7c4cfc6c-f166-471b-be3a-30e881f07c47%2Cservice%3AMESHING%2Cstrategy%3A16&sh=1
There’s definitely things I encourage you to play with, like domain size, bounding box resolution, refinements etc.
In this project you will also find a converged run using the draft mesh. I chose to use a combination of velocity inlet and a custom outlet BC but there should be other combinations possible (and more representative than this one even).

/Ric

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Okay thank you a lot, I used a lot of what you did and it workded !

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Hello, I am a bit sorry but I have another issue as soon as I change the mesh parameters the mesh is computed correctly but then there is an error with no explanation why in the simulaion.
https://www.simscale.com/projects/WarChitect/helicetipe2/

You didn’t have a mesh selected for the errored sim runs…

Oups, sorry

Hi @Ricardopg and @jousefm thank you both for your support last time on this Forum. Please I need some help with another model- a CFD model for flow on micro wind turbine and am still new with this. Am trying to get the flow around the wind turbine based on different pitch angles like 15 degrees, 20 degrees, 30 degrees? :sunglasses::grinning:

The first model is here while the second model is also similar.

At the moment, I set up these two different models for this same problem, and would need advice on the right way to st it up. You can work on it and let me know how to get on with it. In addition, I was trying to use MRF but it seems I was gettig somethig wrong.

Lastly, for the results obtained, the velocity and pressure profiles are low or not showing up well. What could be the reason? How do I slice it up better to show the flow and stream lines in the postprocessing?

Also, is the enclosure size good for the model or what do you suggest on how to better capture the wind speed on the micro wind turbine blades? Is the mesh type used also the best to use for this? Thank you.

DonVic

Hey,

There should be a 100% solid volume (in your case a cylinder) enveloping the turbine blades, otherwise you won’t be able to set up the rotating zone:

It should be like this around the blades (picture from this step-by-step MRF rotating zone tutorial):

Furthermore, you definitely should make your enclosure larger, especially up and downstream. It’s too short.

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Thanks so much for this helpful comments, I will update the model as advised.